1. The Field of the Invention
The present invention relates generally to systems and methods for measuring and/or resecting bone, and more particularly, to systems and methods for measuring and resecting spinal facets for replacement with facet prostheses.
2. The Relevant Technology
Many people experience back pain. Back pain is not only uncomfortable, but can be particularly debilitating. Many people who wish to participate in sports, manual labor, or even sedentary employment are unable to do so because of pains that arise from motion of or pressure on the spinal column. Such pains are often caused by traumatic, inflammatory, metabolic, synovial, neoplastic and degenerative disorders of the spine.
One of the most common surgical interventions today is arthrodesis, or spine fusion, of one or more motion segments, with approximately 300,000 procedures performed annually in the United States. Clinical success varies considerably, depending upon technique and indications, and consideration must be given to the concomitant risks and complications. For example, spine fusion may decrease function by limiting the range of motion for patients in flexion, extension, rotation, and lateral bending. Furthermore, spine fusion may create increased stresses and, therefore, accelerated degeneration of adjacent non-fused motion segments. Additionally, pseudoarthrosis, as a result of an incomplete or ineffective fusion, may reduce or even eliminate pain relief for the patient. Finally, the fusion device, whether artificial or biological, may migrate out of the fusion site.
Recently, several attempts have been made to recreate the natural biomechanics of the spine by use of an artificial disc. Artificial discs provide for articulation between vertebral bodies to recreate the full range of motion allowed by the elastic properties of the natural intervertebral disc which directly connects two opposed vertebral bodies. However, artificial discs do not fully address the mechanics of motion of the spinal column.
In addition to the intervertebral disc, posterior elements called the facet joints help to support axial, torsional and shear loads that act on the spinal column. The facet joints are diarthroidal joints that provide both sliding articulation and load transmission features. The facet joints also help to maintain the appropriate level of stiffness in the spinal column in all planes of motion, including flexion and extension, lateral bending, and rotation.
Recently, some procedures for replacing facet joints have been proposed. Unfortunately, spinal anatomy is very complex and highly variable from one person to another. Accordingly, making accurate spinal measurements and resections can be very difficult. Spinal resection is made even more difficult by the need to avoid nerve roots positioned in close proximity to the bony features that are to be resected. Facet joint replacement adds additional difficulties because the facet joints articulate to provide three distinct planes of motion. Accordingly, replacement of the facet joints requires that each plane of motion be reproduced in order to accurately preserve the natural biomechanics of the spine. Hence, a need exists for systems and methods that facilitate accurate measurement and resection of spinal bone tissue.